> Do note that these emissions do not occur often, think about up to 10-100 per hours in stress states.

I think I must be misreading. If one wants to detect these signals being emitted by plants, why is 10–100 per hour not often? I'd think that having to wait 6 minutes, or, to play it safe, even an hour would still be way more informative than finding out about the stress only when its effects were visible to the eye.